【Spring】Spring中的DI（依赖注入）Dependence Import

由之前的IoC可以知道，我们写在具体对象后面的new方法肯定不能要了，这时候就要通过依赖注入的形式将Dao配置到Service中
Dependence Import的步骤如下：
1. 在Service类中给Dao提供setter方法

原本我们是直接给bookDao new了一个对象

public class BookServiceImpl implements BookService {

    private BookDao bookDao = new BookDaoImpl();

    public void save(){
        System.out.println("book service save...");
        bookDao.save();
    }

}

修改如下，给bookDao设置一个set方法（在IDEA中在bookDao上按Alt+Insert可以快速生成set方法）

public class BookServiceImpl implements BookService {
	// 第一步：删除原本的new方法，给bookDao设置一个setter方法
    public void setBookDao(BookDao bookDao) {
        this.bookDao = bookDao;
    }

    private BookDao bookDao;

    public void save(){
        System.out.println("book service save...");
        bookDao.save();
    }

}

2. 因为我们是在BookServiceImpl中使用到了bookDao这个对象，我们要使用bookDao的bean来对这个对象做初始化，所以我们在Spring config文件下做配置

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    

    
    
    <bean id="bookDao" class="com.example.demo231116.dao.impl.BookDaoImpl" />

    <bean id="bookService" class="com.example.demo231116.service.impl.BookServiceImpl">




        <property name="bookDao" ref="bookDao"/>
    bean>
beans>

我们要在bookService中配置bookDao这个对象(name)，参考的是id为bookDao的bean(ref)。
结果如下：

######################
完整代码：

BookDao.java:

package com.example.demo231116.dao;

public interface BookDao {
    void save();
}

BookDaoImplt.java:

package com.example.demo231116.dao.impl;

import com.example.demo231116.dao.BookDao;

public class BookDaoImpl implements BookDao {
    public void save(){
        System.out.println("book dao save...");
    }
}

BookService.java:

package com.example.demo231116.service;

public interface BookService {
    void save();
}

BookServiceImplt.java:

package com.example.demo231116.service.impl;

import com.example.demo231116.dao.BookDao;
import com.example.demo231116.dao.impl.BookDaoImpl;
import com.example.demo231116.service.BookService;

public class BookServiceImpl implements BookService {

    // 5. 删除使用new建立对象，
    // 6. 同时建立set方法
    public void setBookDao(BookDao bookDao) {
        this.bookDao = bookDao;
    }

    private BookDao bookDao;

    public void save(){
        System.out.println("book service save...");
        bookDao.save();
    }

}

Deomo231116Application.java:

package com.example.demo231116;

import com.example.demo231116.service.BookService;
import com.example.demo231116.service.impl.BookServiceImpl;

public class Demo231116Application {

    public static void main(String[] args) {
        BookService bookService = new BookServiceImpl();
        bookService.save();
    }

}

applicationcontext.xml:

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    

    
    
    <bean id="bookDao" class="com.example.demo231116.dao.impl.BookDaoImpl" />

    <bean id="bookService" class="com.example.demo231116.service.impl.BookServiceImpl">




        <property name="bookDao" ref="bookDao"/>
    bean>
beans>